Update: According to documentation cp850 can not be used in ussd reply (at least with dsc field 15). On the other hand, our implementation shouldn't work at all, because we expect (and we get!) 8 bit encoding, while we should get 7 bit encoding. I would appreciate, if you try running these commands in pnatd: at+cmgf=1 at+cscs="IRA" at+cusd=1,"<your USSD number>",15
They should produce a lot of digits instead of human readable reply.